The long term objective of this project is to characterize how intratumoral heterogeneity is influenced by tumor suppressive mechanisms. Specifically, the consequence of p53 loss on the development and maintenance of cell-cell genetic diversity will be investigated, based on preliminary data from mouse models. Intratumoral heterogeneity produces a substrate for evolutionary selection and adaptation to a changing environment, for example, as cells disseminate to a new site or are challenged by therapeutic intervention (13). Acquired resistance to therapy is a major roadblock in achieving durable cures for B-cell lymphomas and other cancers (4). In many contexts, resistance has been shown to originate from pre-existing drug-resistant subclones (19, 20), and thus, the level of genetic variation in the tumor underlies the robustness of the tumor to clinical intervention. Central Hypothesis: As genetic abnormalities occur, they have a greater probability of persisting in the population, as a lack of p53 levels the playing field by reducing the differences in relatve fitness between a broader array of otherwise nonviable genotypes. The inevitable result is the accumulation of intratumoral heterogeneity. Specific aims: 1) Intratumoral genetic diversity of a collection of human diffuse large B-cell lymphomas (DLBCLs) will be measured using a single cell sequencing approach (29). The association of heterogeneity and p53 status will be investigated. 2) The role of p53 in the development of heterogeneous lymphomas will be functionally evaluated in a mouse model of B-cell lymphoma. 3) The mechanism of intratumoral heterogeneity will be explored by lineage tracing and by inactivating various p53-related sensors and effectors to determine if modification of a variety of p53-realted processes, including the DNA-damage response, cell cycle control, apoptosis, and lineage commitment, can recapitulate the diversity phenotype achieved with the loss of p53. Training Plan: The applicant will rely on an interdisciplinary team of mentors and collaborators to develop an expertise in cell & molecular biology, mouse genetics, and computational analysis of genomic data. Sufficient oncology clinical exposure will be pursued to optimize the relevance of laboratory investigations and to obtain the skills necessary for cultivating future clinical and translational partnerships. Implications/Relevance: This fellowship will effectively realize the goals of the NIH by fostering creative and innovative research regarding the cause and cure of human disease (i.e. treatment failure), and by developing the applicant to contribute over the long term to the Nation's capability to prevent disease and economic well-being through biomedical innovation.